The National Toxicology Program (NTP) seeks to assess risks associated with possible acute, repeated or chronic exposure to chemicals by investigating a variety of biological effects including carcinogenicity indiced on chronic exposure. Studies of the mechanism(s) of toxicity and the fate of chemicals in intact animals are an integral part of the range of NTP studies designed to characterize chemical toxicity. Data obtained from studies of the fate of chemicals in intact animals, as described in this contract, support NTP objectives by providing the fundation on which extrapolations of risks from laboratory animals to humans are based. Objectives of this project are two fold. Each study is designed to address those physical and chemical properties unique to the compound studied as well as to provide data that will permit structural characterization of the respective chemical calss. These studies may also be designed to address the impact of one or more factors such as does, species, age, sex or route of exposure on the fate and/or toxicity of the chemical(s) studied and thesignificance of thede data to assessments of human helath risks. Thus, the immediate objective of these studies is to determine more accurately the doses for NTP bioassay studies. The long-range objective is the accumulation of data that will permit better assessments of those structure-activity relationships that determine chemical absorption, metabolism and disposition in laboratory animals. The ultimate objective of this project is to provide data that permit better assessments of risks associated with human exposure to chemicals encountered in the environment, home and workplace.